There are numerous known methods for extracting oil from vegetable materials. One techique in commercial use, for example, involves continuously pressing the vegetable material at low moisture content to expel oil. A pretreatment steaming of the vegetable material is frequently employed to facilitate the pressing operation. In addition, it is common to employ a subsidiary step of solvent extracting the pressed material to remove residual oil.
Unfortunately, these processes possess a number of drawbacks. In particular, the expelling operation requires heavy machinery and results in a substantial rise in temperature harmful to oil and vegetable protein qualities and further tends to produce large quantities of vegetable fines which must be separated from the expelled oil.
Other techniques designed to circumvent these drawbacks have been found. These include the processes set forth in Canadian Pat. No. 763,968 and U.S. Pat. No. 3,786,078. Both of these patented processes involve direct extraction of the vegetable material with an oil solvent. Because of their respective requirements of severe operating conditions, extraction of finely divided material and/or complex pretreatments of the oil-bearing vegetable material, however, they have not proven altogether successful.
It is therefore an object of this invention to provide a simplified process for recovery of oil from vegetable materials.
It is a further object to provide an oil extraction process which does not require subjection of the oil or vegetable material to deleterious conditions of operation.
It is a still further object to provide a process which permits essentially complete recovery of oil from a variety of vegetable materials.
Another object is to provide a process which does not release finely divided material into the oil solvent.
In a copending U.S. application, Ser. No. 95,743, filed Nov. 19, 1979, a process is disclosed which involves subjecting moist vegetable material to pressure sufficient to rupture the oil-containing cells without expelling the oil from them. The compressed material is dried and the oil is extracted with an oil solvent. While this procedure overcomes many of the problems associated with earlier processes, it gives material of very low bulk density which is hard to handle on a large scale and which requires bulky oil extraction equipment. It is therefore an additional object to provide a process with extractable material of comparatively high bulk density.
These and various other objectives, as are apparent from the description which follows, are achieved through the present invention.